So I'm not sure where you are located, but in south east Pa, my lillies and bog ploants are starting to grow. I usually will just repot anything that looks to be creeping out of the pots. I sometimes divide the lillys and give them away.If she has bog plants like cat tail, you can cut all that old growth off. All the goo will certainly clog the pump filter. I use a foam filter to protect the pump and rinse it often. Eventually though, it will end up being a bucket project. I take something to scoop and two large buckets and just fill and dump those buckets. They can get really heavy when they are full of mud and sludge. If you have a helper, that makes the task much easier..one to scoop into the buckets and one to dump them..Dont fret too much over the plants because they usually survive the cleaning really well. Ask about frogs because I always rehome all of my frogs. They are cute but they eat fish, especially the american bull frogs (I have one in my pond right now that could eat a small child).