Juice,
It can be done but will require some forward planning on your part.
Your DD will be on your lap for take off and landing (the aircrew will provide you with an extendable belt for this purpose). You may be able to get a bulkhead seat and a bassinet for DD to lay in - again this is dependent on the airline you use.
Some general pointers:-
Try to get a direct flight to your destination; you do not want to change planes unless you really have to.
Choose a UK based carrier over an American one.
BA are good but you will not be able to use their online check in facility as you are travelling with a child.
Take some toys that she will like although ensure that they are not tiny (if dropped you may not see it again).
Change her nappy before you board. Those airline toilets are very small even though there is a change seat in there.
Tie something brighly coloured to the handle of her pushchair (along with the luggage label) so you can recognise it more easily. Such items can be taken to the door of the aircraft and then placed in the hold. Ask them where it will be collected (sometimes it is usually at the door of the aircraft on arrival).
Do not rely on the airline to provide adequate food for the journey; take some yourself for your child. Children's meals are not served much before the food for the adults arrive.
Take full advantage of early boarding (this is usually done for families and the first class passengers).
Usually flights to the US depart during daylight hours; return flights from the US fly overnight arriving in the UK the next morning/afternoon.
Your DD must have her own machine readable (these are passports with two lines of info on the back page) passport to enter the USA. Children will not be fingerprinted and photographed on arrival into the US (all adults are) but you must complete a green visa waiver form for her (all passengers need to complete such a form; these forms will be given to you at check in).
You must have your own machine readable passport to enter the USA.
HTH and good luck