It's too early for the pretty summer bedding that is appearing in the shops now. These must be kept frost free, and there is always a risk of a frost until nearly the end of May. Perennials are plants and shrubs that will/might die back and re-grow the following years - these plants don't look pretty yet. Read the labels and look on the RHS web site for their how-to plan your planting guides. Do you want to dig a border or plant in tubs? Or make a raised bed depending on budget? If you buy pots/tubs, always get the biggest she can afford, and make sure they are frostproof. Without knowing the soil and the aspect, it is hard to recommend specifics. but it is lovely that you are helping your neighbour