Thanks for posting your query.
From your description it appears that your mother probably had a temporary blockage of a salivary gland
duct. The sublingual salivary glands are present under the tongue.
Possibly the act of chewing the food dislodged the blockade. That would explain the gush of salty fluid she experienced.
As she had the lump for just a day it was probably not infected.
But if she has another such episode it would be best to see your doctor to rule out an infection.
In the meantime it is important to keep your mother well hydrated. Encourage her to drink plenty of fluids as dehydration
can predispose to duct blockage.
See that she maintains good oral hygiene