You will get lots of specific mentor training as part of the ECF. That will help you know how best to help her improve her teaching skills. You might find though that the formal side of all that doesn't kick in until three or four weeks into term.
The things that are less tangible, but vital, to support with are the unspoken rules (the things people will tut at but nobody ever actually tells you about!), how to get things done (eg photocopying , ordering a school lunch if you forget), helping to make connections around school if she's on the reserved side, and making sure she takes a break and eats lunch.
If you can be available for a couple of specified days in the holidays to answer questions or look at things she's doing to get ready, that will help reassure her she's not alone. Letting her know what will already have been done before the year starts (eg have her books been labelled, will she have a stationery supply?) and any other practical tips that will save her unnecessary prep work.
And keep an eye out early on. If she's going adrift, it is far easier to help her get back on track sooner than later Eg if she's doing stupidly detailed marking, or not getting through enough readers, or children getting let out late. And also you can then catch her doing good and find lots to praise 