She needs to be sure the benefits people will accept a year's rent as a legitimate expense and not expect her to live on it completely for several months first
It may be different in other areas where rented properties aren't so hard to come by, but I have helped clients do this and explained to the DWP that because of their poor credit/being on benefits, the only way that they could get a property was by paying 6 or 12 months rent in advance.
It's never caused a problem.
However, I think your daughter would be wise to consider returning to work when she's had the baby and buying, if the sums add up. I suppose it all depends on whether you live in the absurdly expensive south or somewhere where property is cheaper.
Are you allowed to release funds early, OP? When my DSS inherited £40k from his GM, it was held in a trust until he was 30, unless the trustees (his parents and GF) agreed otherwise. By the time he was 21, the original £40k was over £100k and he wanted to buy a property. The trustees all agreed and he used it to buy a rundown house in Brighton and do it up.
He now has a lovely house and a small mortgage that is more than covered by the rent from the friend who shares with him. He's better off than all of us, and he's not 30 yet!