She's emailed me yesterday about an 2 mile open water swim she's doing in 3 weeks, asking for sponsorship. I emailed back asking how the training was going, and she's not done any as she's self conscious about going to the swimming pool
She won't manage the distance:
2 miles is about 3.2km. That is 3200m which is 128 lengths of standard 25m swimming pool.
It's a fair way. I regularly swim 1km in a pool and I wouldn't think I could just up the distance to 3.2k without training in terms of pool swimming.
Add to that it's open water - what kind of open water and where?
She won't manage the cold if it's in the UK:
If its in the UK, unless there is a sudden heat wave she will need a wetsuit for an open water swim of that distance - and you need to test out a wetsuit before you embark on a long distance swim - to check it fits you properly and it's too constricting.
There are very few places that are so warm that you could do an open water swim for 2miles without a wetsuit - you are basically talking places like lakes in Africa or the Med in blazing August.
If it's in a lake or similar, I think in principle you could manage that if you are a trained swimmer but if it's in the sea, that kind of open water swimming is a really different ball game.
Rather than worry about sponsoring her, I agree that you should strongly dissuade her from doing this.
Do you know where she is "doing" this swim?