Yup - my gym told me the same as Ali said. Maintaining the pre-preg level of fitness is fine but starting out on a big exercise regime for the first time when pg is not on. I am not a runner but was going to the gym before falling pg and in the early days. I ran briefly the other day to stop a door slamming in the wind that I wanted to get through and felt a bit unwell for a few minutes afterwards. I had only just eaten breakfast but I think I am less fit now than I was before.

I think your friend will be fine for while yet - she sounds awesome! She may slow down towards the last few weeks though.