You still wouldn't be able to snow foam with this - you'd be hard pushed to find a lance that fit it, for a start, and even harder pushed still to get it to produce enough pressure to foam anyway! Even if you could get the foam on, foaming is entirely pointless if you can't give it a proper, thorough rinse with a decent water source - the purpose of using a pressure washer is not for the volume of water, but the pressure itself will remove dirt than just using a hose (or this!) in the same way. It might be a bit more hassle but you really will be better off going to your mum's house.
This simply doesn't offer anything useful that I can see. That's just my opinion though, waste your money as you see fit.