Surprisingly it appears there is a Grizel (Stewart) Innes connection to Robert Innes (of Muirton) the General Quartermaster after all. Though he is not her son, he is her son in law:
The baronetage of England: or The History of the English Baronets and such Baronets of Scotland, Vol. 5, by William Betham:
"1. Sir Robert Innes, of that Ilk [i.e. "of Innes"], who was created a Baronet of Scotland, as above.He was made a privy counsellor for life, and appointed one of the committee of estates by the parliament, in 1641.Yet he seems to have been a loyalist, for when he was forced to acknowledge the parliament in 1649, he was obliged to get his eldest son, Robert, to become surety for his good behaviour in time to come.
He married Grizel Stewart, daughter of James, Earl of Murray, by whom he had three sons:1, Sir Robert, 2, James, of Lichnet; 3, William, captain in the guards; and five daughters:1. Elizabeth, wife first of John Urquhart of Craigtoun and was mother of Sir John Urquhart, of Cromerty; secondly, of [James] Brodie, of that Ilk, by whom she had no issue [actually a Brodie genealogy gives 2 children, this is Lord Brodie]; 3 [Grizel], of Sir Robert Innes, of Muirtown; 4, Barbara, of Robert Dunbar, sheriff of Murray; 5, married Alexander, Lord Duffus.He died before the Restoration of Charles II, and was succeeded by his eldest son" [Robert.]
Comments in [ ] above are mine.
Other releavant information that explains who Robert Innes of Muirtoun was and names his wife as Grizel (yes two consecutive generations named Robert and Grizel):
From Polichronicon Seu Policratica Temporum by James Fraser:
"1668. The next who parted this life was Sir Robert Innes of Moortoun, commonly called the Generall Quarter Master, being ingaged in the late rebellion. He sould the reversion of Cromy, and bought the lands of Moortoun and Leuchers, about Kinloss, a bad purchass, church land, borrowd monny to buy it, could not extricat himselfe, turn melancholy after his ladys death, and died himself in March, and left a poor unsolved ofspring. He thought to leave the care of all uppon my Lady Duffus, but her death crusht him, and all evanisht. Many deaths at south this year, Lord Kingorn, Lord Sinclar, Fife, and Angus, whose names I leave to be enrolled in the Bill of Mortality where they lived."
From: The Register of the Privy Council of Scotland it appears the wife of the General Quartermaster is also named Grizel.
"Petition of Grizel Innes, Lady Mourtoun
Grizel Innes, Lady Mourtoun is cited to compear before them at Elgin on 3 February, but as is well known she is in such a condition and so valetudiary that she cannot come in without hazard of her life.She never absented from church without a sufficient excuse, and out of no disaffection to the government or disloyal principles which she abhors with all her heart."
From the Diary of Alexander Brodie, Lord Brodie, a very religious man known for pillaging the cathedral at Elgin, brother in law of Robert Innes the GQ:
"I did send my sone to [Innes of ] Moortoun, to see if he had ani money.He objected myh promis to giv them som favour in the anuel.I desird grac to walk evenli in this promis, that it may be noe snar to me.Therefor all I hav to say befor God for it is this:I did offer it onli, but he did not accept it, nay, since, he hath mani tyms prest land on me for it.2. Things ar now changd in my effairs, for I hav bein put to great troubl since, but was in better cace then to have ans it. 3. I am owing it all, and mor, to others: and I know not if it wer acceptable to God to draw a burthen on myself to spar another, who has it payd in to him, and is as abl to bear his own burthen, as I am to bear myn. 4. I hav som freidom to put it yet in his will to doe in it as he thinks fitt.Now, though I hav some clearnes, and had some clearnes in it, at Edinburgh, quhair Moortoun offerd it, yet I am jelous and suspicious off ani thing that may be a snar to me, becaus I am bound up from usurie for money of my own, and lent to thes that ar in distress, and not to thes that tak it from others, and maks benefit of my moneye." - much more as his brother in law's poor finances troubled him for quite a while.
Add this to the information from Burke's Landed Gentry (Document E)(Robert Innes of Muirtown, the General Quartermaster, is the son of Robert Innes and Elizabeth Pitt, and nephew of "Craig in Peril" Innes) and the genealogy of both Innes lines is traceable quite a ways back for both the GQ and his wife.
Finally on the children of Robert Innes of Innes (m. Grizel Stewart) from "Records of the Parliament of Scotland"...
At Edinburgh 15 August 1662
Sir Robert Innes of that ilk, James and William Innes, his brother, who pretend right thereto by private alienations and dispositions unconfirmed made by the said late Archibald Campbell to them, and after the committing of the crimes for which he was forfeited [Campbell executed for treason, 1661], at least Sir John Urquhart of Cromarty as having right from the said Sir Robert Innes and his said brethren, peaceably possesses the said lands and uplifts the duties thereof without all law, equity and reason; humbly therefore, desiring a warrant for summoning of the persons complained upon above to compear at a certain day, bringing with them the writs and titles whereby they pretend right to the lands and others foresaid to be seen and considered, and to hear and see the same declared void and null.
The Records of the Parliaments of Scotland to 1707, K.M. Brown et al eds (St Andrews, 2007-2009)
That Robert Innes and Grizel (Stewart) Innes were loyalists seems to be of little doubt:
"Upon the execution of Charles I, Scotland failed to recognize the new English Republic of Oliver Cromwell. Instead, it insisted that Charles II was his father's rightful successor. However, this support came with strings attached. It was under the condition that Charles sign the ‘Solemn League and Covenant'. This was basically a promise not to remodel the Church of Scotland, governed by Presbyterian principles, along Anglican lines. Charles II was proclaimed King of the Scots in February 1649. This happened in his absence, since he had been exiled in France and the Netherlands since his father's death. He did not arrive in Scotland until the 23rd of June 1650. His landfall was the River Spey and Garmouth.
The journey from The Hague had been uncomfortable. The king had passed 22 days avoiding Cromwell's navy and only narrowly missed four Parliament ships in the Moray Firth. The tide must have been out and the king had to be carried ashore on the back of a boatman called Milnes; his descendants were known thereafter as ‘King Milnes'. Apparently, the king bestowed a kiss on the boatman's pretty daughter (also called Maggie?). The king was met by Sir Robert, Laird of Innes, and his wife, Lady Grizel, and after an early dinner in Garmouth, slept the night at Gordon Castle."
J. Quinn (most documents from Google Books on-line)