Is she in work?
Does she have assets?
Has she spent the full £4k?
You can always sue her at the small claims court. It is a sum under £10k.
If she is in work then she will be worth suing.
It is worth sending her a letter before action first though.
It will protect you from cost and may well cause her to start repaying.
Can I clarify anything for you?
It is not expensive.
It is not particularly quick but it is a lot faster than quite a lot of other actions.
Yes, keep paying. You are still liable to them as normal.
You could ask for the interest if it was part of your agreement.
I'm just off for about an hour now but I will be back on then if you need to know anything else.