If you maintain your US bank account, she should be able to make deposits directly to your account if she wants. You can then extract the funds here via a cash point. According to Clark Howard (brilliant but practical US economist), the cheapest exchange rate is found by simply withdrawing cash at an ATM. There may be other consequences to this that I have not fully investigated yet, but in the short term this may be a good option for you. Some banks will allow you to change your mailing address to the UK. I use VyStar which is just a little credit union in the deep south, and they changed my address to the UK on my account and were very accommodating with the whole thing. Their online banking allows me to set up email alerts to tell me my balance on set days, even every day if I want, and alerts for other things as well, and I can deposit a check by scanning it in online as well, so it makes long-distance banking almost sinfully easy.
Alternatively, if you set up a Paypal account here (UK), and get the attached debit card as well, your mother should be able to send money to your paypal account which you can then convert directly to £ within the account and use your card like any other card. This won't be accepted everywhere, but it is accepted most places. I've purchased airfare this way, but I can't get a hire car with this card. Makes little sense, I know, but as long as your mother isn't your only source of funds, this shouldn't have too great a negative impact on you. Just don't set up the paypal account until you get here because a US account won't work well in the UK and you can't move the account from one country to another.
Or.... make sure you have a bank account before you go that is housed in a bank that operates in both the US and the UK, so your account will transfer when you do. And then just go with option 1 from there.
I've only been here a few months, and am not here permanently yet, so there are many many people on this site who will likely have better information than I do, but these things have worked for me so far. Maybe they'll at least get you over the hump, so to speak.