This is what I was thinking too. The only question mark is the 10:30 start and 2.5 hour ascent. It doesn’t look on the map that it would take that long, so I wonder if she looked around (checked out the two refugees at PdE and LB, maybe looked longingly at Maladeta glacier).
What time was it she texted Dan saying she had hitched and was “half way there”? It must have been before she lost signal at the end of the road.
So, here's my next layer of speculation.
When ED was at the Cabane de Besurtas, she decided to try for the glacier on 11/22. It didn't work out for some reason.
Somewhere in the foray to the glacier or on the way back or at lunch or the stay in the Cabane, she met someone who was also interested in going up to the glacier. If they went together, they could look out for each other.
This might have been a plan, a thought, an idea, whatever, but ED was tossing it around in her head.
She climbed back up to the Pic undecided about a whole lot of anything, really wanting to go to the glacier and having a kind of half-baked back up plan to the Glère or something, she didn't even really know.
While she was on the Pic, she saw the glacier right in front of her, things came together for her, and she decided on the fly to try to reconnect with the person she met at the Cabane and make it up the glacier.
Then for some reason the "connection" didn't work out.... either the person wasn't at the Cabane any more, or they set off together and got separated, and she had an accident or..... This doesn't have to be foul play, although that's possible, too. It could just be things weren't firmed up with the other person and/or didn't work out. ED could even have made it onto the glacier on the 23rd but lost touch with her "friend", and then had an accident.
Since the Cabane didn't have phone service, ED wouldn't have been able to communicate with anyone there, even though she had service on the Pic. So the idea to go to the glacier with this unknown "friend" could have been very vague.