The blood from the mouth comes from the second wound (the one under the chin) which was undeniably instantly fatal. It's "flowing" because it's leaking out through the hole in the bottom of her mouth through gravity.
A coupe of things to bare in mind, is that the raid team entered at 7:30
The photographs were taken just under two hours later just after 10am and there were also a 2nd set taken in the main bedroom later on.
One of the reports from the raid team said her blood was leaking, not all of the raid team entered the bedroom and saw Sheila.
However, this would mean that she would have been shot after Jeremy had arrived with the police.
If she had been shot before 3am all the blood would have been cracked even that on her neck, but it wasn't....
The only other thing I can add, is the partially digested food and the fact the poor lass looked remarkably clean....So, if she had gone to her mother, then why did she not help her or hug her? If she had done this then she would have her mums blood all over her.....