OP oooh I'm only on page five of 11...it's a risk posting I know BUT:
what one poster said early on is the most relevant here, think it was halloween
I think you should tell them that while you would have normally been happy to help for short trip, for such a long journey requiring lots of planning on everyone's part and hte potential for things to not go quite as planned you think it's too much of a risk/not really practical both for her and you to try to commit to such an arrangement.
What if your plans change and she's arranged herself to fly around you, what if one of you gets chucked off for overbooking etc as Halloween mentioned (you woulnd't be able to stay behind with her given limited time off, etc) Among any possible scenario.
You think it's better if the AIRLINE is lined up to help her in case an unexpected scenario arose as they are more experienced. You don't want to let her down.
I am willing to bet they don't even realise such a service exists, the assisted travel thing.
If they won't go for that and say they want YOU to do it, I think it's fine to say no, sorry, I just don't feel comfortable.
If it were me travelling or my mom or dad I would feel much more secure if this were in place.