Lola has been on and off licking her rear leg by the bendy-bit

when I've looked under the magnifying glass there is a little lump which made her flinch slightly when I touched it.
Do you think it could be a dreaded grass seed?
I would like to try silica first of all but have a couple questions:
Can you buy it over the counter at the chemist?
One table once a day do you think?
and finally it won't do her any harm even if it isn't a grass seed will it?
Thank you.