You can't fix her, you are not trained in mental health. You won't know the times when your input will be enabling her or harming her by lending credence to a delusion.
Have the words treating them would be a bottomless pit been heard from you directly from a senior health professionals mouth?
Is what they meant actually they haven't the money to deal? Or more a reflection on the possibility that at this point your friend is being her own worst enemy as she currently doesn't want to face her issues and has no interest in getting well at this time?
Does your friend hoard animals? Animals are in no position to be an emotional crutch for someone, they need love and care themselves. Where the mental health professionals seeing she had too many balls in the air with them and was beginning to neglect their primary needs for care?
While animals can be towers of strength for their owners emotionally, they are not a substitute for something that is seriously lacking in their own mental stability. It is unfair to ask them to fill such a hole and like you say when it all falls apart they may well ultimately answer for it with their lives. The real question here should not actually be are they your friends life line and do they keep her going and are her only reason for living? More is she providing them the care and support they need, even animals can't be all give, they need love in return as well.
This is a complex situation OP and you can't use a love will conquer all attitude as a band aid and say it will be ok, it won't. I am not saying don't help her but you need a hell of a lot more information about what help you need to be offering her and what may initially be seen by you as help but which may actually make your friends situation worse.
Refusing to see the finer complexities and seeing that for some people they have to walk away as the illness is selfish and will demand they sacrifice everything they have to your friends needs and just saying they didn't have enough love or weren't very nice is not seeing the bigger picture.
Giving yourself over to your friends every whim is not being there. Doing whatever she asks is not being there and not being constructive. If you really care and want to do something you need to approach the mental health professionals and find out exactly what her needs are, then be her advocate and harass and harangue the health authority to ensure she gets that help. They will always help those who shout loudest over those unable to speak for themselves unfortunately. Being her shield against the world and knight in shining armour will not do her any favours and will exhaust you to a point where you cannot physically function. What will she do then when you have fallen apart yourself?
Just throwing your hands in the air and saying they won't help is going to land more on your shoulders, you are not Atlas. They have to be pushed to help and you have to recognise that the help your friend needs and the help she wants may be two very different things.
Don't delude yourself that you can do it alone this will be very harmful to your friend in the long run. Educate yourself about her illness and be one of her ports of call for aid, not the only port of call. Its not called a support network for nothing as we all have off days and she needs people to be there and one single person no matter how much they want to can be there 100% of the time. You will have emergencies in your own life which coincide with hers, her need will not wait and she will not understand this so you do need other agencies and people involved to take over. If she demands you to be her only support, compelling though she may be and no matter how much you want to do it you do not have the strength, no one person ever can. No matter how nice, saintly, loving, religious, compassionate or whatever else may be driving it.