As mentioned,cs/pepper spray is a section 5 firearm.I know you had the best intentions,but I would get it back off her and please don't advise her to carry any kind of bladed article-screwdriver etc (again,I understand the best intentions that are meant).
This situation already means that she is probably a nervous wreck,so arming her could mean disaster-to her if she gets caught with a can of incapacitant,her kids if they find and use it by accident or,in the worst scenario,she has it used against her.
Ask the Police to put a warning marker against her address-this will mean that any calls from her address are treated with priority.
The Police can,under certain scenarios,install cameras and at the very least,DV alarms with panic triggers on either a personal fob or somewhere in the house.I would argue that if this situation is as your post,this is one of those scenarios.
I would also go with the pir advice and fit alarms to the windows.Also,check that her door and window frames are solid.
Ask her to tell her immediate neighbours about what's happening.If they are aware,they will be an extra set of eyes for her...
Good security advice and support from both yourself ,friends and the Police will be better than giving her a weapon.
Get her to keep a diary in an A4 book of ALL events,however trivial.This may assist in providing a statement later down the line.
Hope all goes well...