If she has shells for it, read the box. If there is no box, read the stamping on the base of the shell.
It is probably an obsolete .32 Long cartridge -- possibly .32 S&W Long (SNL) which is available from Federal. .32 Colt -- which is slightly narrower -- can be obtained from "Old Western Scrounger."
Have someone who knows what they're doing ascertain the proper caliber and check the timing before attempting to fire it -- which should probably be done by duct taping the handle to a fencepost and tying a length of fishing line to the trigger. If you wish to store it loaded, keep the hammer down on an empty chamber, as these guns have no firing pin (it uses a spike on the hammer) and may discharge if dropped.
.32 Long has less stopping power than a .32 ACP or a .22 WMR -- it is a very poor choice for CCW -- if you shoot someone with it they may become rather cross with you. I have seen bullets in this caliber bounce off boards, fenceposts, and trees. They will not penetrate a leather jacket. If you put it to your temple and pull the trigger, you've got a 50/50 chance of turning yourself into a vegetable. Gramma's gun is garbage . . . sorry.
Meridian .32 revolver in excellent condition may be worth about $75 -- see if you can trade it in for credit towards a NAA Black Widow in .22 WMR or a KelTec in .380.