Congratulations on your new addition to the family - I hope that you'll have several happy years with her.
It will all be strange for her - particularly if she's been in a quiet home and is moving to a bustley family home. Try to make sure that she has a 'safe' preferably quiet place that she knows is hers and won't be 'invaded', and preferably have things in it that she's familiar with (eg basket).
I would plan on 2 meals a day - find out what she's been eating and try to start off with that, even if you gradually swap to something else. I like feeding a good-quality all-in-one because I know its been formulated to provide what the dog needs - I'm using James Wellbeloved for the first time with our new dog, and know many other people that use that, although there are plenty of different foods that you can choose from. Aim to get one that guarantees the ingredients so that you don't get a different quality depending upon what is the cheapest meat around that day.
You might want to look at a 'senior' dog food given her age.
Look at the feeding quantity and work out how you're going to measure it (we use a beaker as a scoop, having worked out how many our dog needs over the day). Remember if you use treats you need to knock off some of the food if you're trying to help her lose a bit of weight.
Take her to the vets and get some advice on what weight you should be aiming at and how long it should take to get there (and make sure any innoculations are up to date and worming).
You might need to build her up gradually to decent length walks - she might not be fit enough and her pads might not be tough enough either to start with.
Don't let the children go near her when she's eating - strict rule - even if she seems OK - its just not fair.
HOpefully you'll inherit her brushes etc too - otherwise you'll need them with a spaniel - little and often is probably the way to go. Stockpile old towels for the back door to wipe muddy feet.