You never know, she might remember. It’s always a toss up. Legally you are up the proverbial manure creek. It’s just not allowed to tamper with someone else’s work without express written permission bladibladibla.
On the other hand if you put out a really awesome remix you might get noticed by someone (including the original artist) or you can just get slapped with a take-down notice and a stern message from their lawyer.
I doubt you’ll be successful in acquiring stems or even acapella’s, but it’s free to ask, right?
Then again, asking for permission has two distinct disadvantages, while the chance of success could be relatively small. The first is that you’ll draw attention to your plan, so while you might not even get a reply, you’ll be on the spotting list. Second, you might just get a flat out NO and then what? If you decide to put out the remix anyway, they’ll have no problem proving you did so DESPITE explicit instructions otherwise.
This is all clearly on general terms. I’d see if could somehow wiggle her liking your instagram photo into some sort of informal contact where you could, just in passing, query how she feels about people doing remixes of her work.
At the end of the day, it’s your call.