She sounds like Lilith a bit: first woman of the creation, and once she chooses to follow her own path instead of getting along with her man (Pemba or Adam) she becomes a demon spreading disease or fear by attacking new born... Probably so that women would take that as a cautionnary tale, haha...
I believe that even in darker sides of deities, there is a positive message to learn. You need chaos to create order. Tarots cards also put the death arcana in the middle of the pack (no 13), as part of a cycle of change and self improvement, as some things in you need to die so that you can progress and renew yourself. It is not an end but a passage, like an initiation. It is perhaps also in darker times that you learn most about your strengths and limits too. Your friend shouldn't feel threatened by such a Goddess but learn her lessons, perhaps go beyond despair or anger, direct the energy of anger towards a positive goal, and the sadness or despair towards compassion to others?
The goddess Kerridwen has three sides too: energy of youth, fertility of a mother, and crooked old death.
I find her connection with Leopards very interesting personnaly, as I believe my animal guide is Leopard. Since she presented herself to your friend in that shape, perhaps your friend needs to get to know leopards. They are graceful, persistent, patient, strong and quick. Your friend should practice patience with her/his present situation, and perhaps also look at the source of all these current problems she/he is facing by "stalking", researching and finding a solution to make it come to an end. Your friend needs also the strength of that animal (it can lift its preys up in trees to eat peacefully without any other predators to steal the meat). It is also a solitary animal, so your friend might also need some time alone to figure out all this, meditate, plan a strategy etc. Perhaps the goddess under her Leopard shape is telling her the way out and leopards have come as advisors. In that case the goddess has become a powerful ally and she should be thanked.