If I were you, I'd call the nearest dealer to find out how much it would cost for the memory cards for it. You need a ata compact flash adaptor.
You can buy your own designs or get them for free - there are a ton out there. I will say that chances are, you would not have wanted the designs she had unless they were really good ones but that's a mute point now, aye?
I am not sure how much that adaptor or more memory cards cost. If I were you, I would ask the lady if she has at least that adaptor thingy...
Do a search here on the site for the 300e and email a few people to see how much the memory cards are and if you need to replace the adaptor gadget how much that might be.
The Janome is a good one. I started off with the 350e which is the upgraded version of the 300e.
They still sell the 300e... I believe it sells for about $800 or $900 so it is a great deal - You will need at least two of the cards and one of the adaptors. It looks like you can get the adaptors online fairly cheap. You'd probably be spending another $100 in cards and adaptors.
Start stock piling the free designs - emblibrary has them once a month as does Urban Threads (they have much more modern/stylish designs for the most part) I think it's a good deal especially if she is throwing in the threads, stabilizers, etc. The thread and stabilizers will cost a small fortune to get up and going but you can get great deals on ebay. I have always used polyx40 thread since it is what my local Janome dealer stands by - you can get great deals on it online for entire sets of colors. The stabilizers are must haves. You can not embroider much without them... They can be costly but it is necessary.