I'm sorry to hear your dog has been so unwell.
There are several things which you mention that ring alarm bells for me.
A temperature of 35.8' is extremely low and can indicate shock and poor circulation. This can potentially lead to organs shutting down.
Similarly, if her heart beat is truly 46 this is critically low. A dog of her size would normally of a heart rate of at least 80 bpm. Again, this tells us her circulation is poor and she is really struggling.
She is in a critical condition and needs urgent care. Subcut fluids will not be enough, she needs intravenous fluids immediately.
We also need to find out exactly what is going on as this is highly abnormal for such a young dog. I would be considered about toxicities, addison's disease, pyometra (if not neutered) etc.
Not only does she need to be brought to a 24 hour clinic for stabilisation straight away, we need to find out what is going on to start any necessary treatment. At a minimum, she needs blood and urine work.
I'm sorry I cannot be more reassuring or offer advice for home care but she needs to be seen right away. Please let me know if you have any further questions.