If the amount of the gift is in any way a function of the amount that Bob has earned for Jill, it raises flags.
Perhaps in isolation, any single fact you’ve laid out about how much better Bob has done for Jill than an ETF, or the total return, or how she wants him to continue wouldn’t matter that much. But when taken together, it definitely raises flags.
Query: what would Jill do if her returns were the same as an ETF? Less than an ETF? What would Jill do if Bobs investments had lost principal? Whatever the answer to those questions is, That’s what Jill can do for Bob.
If I were Bob, I wouldn’t accept anything more than that. I would also stop doing this Kind of advising for any friends.