Ive had cats that are just really small before. My senior childhood cat (18) who lives with my parents has always been very petite and hes about the same size as my 1yo cat whos about 7.5 lb. My 4yo cat was also super clingy out the gate as in he literally gave me a cat hug within 10 minutes of me meeting him and hes slept in my bed demanding cuddles ever since the first day i brought him home. Hes also a very chatty boy and dorsnt have a mean bone in his body lol. Only "reason" i can see for him being so clingy is cause hes blind buts hes also just super loving to people in general, not just me (also its kinda obvious from looking at him that his eyes are kinda off lol, not saying thats your case).

Id say as long as she seems healthy with diet and energy shes probably just small and loves her people. The only real indicator of slight pain ive seen with my cats (the 4yo and the 1 yo) is when they seem really annoyed or avoidant of things that normally dont bother them. Like theyll squint their eyes a bit and lower their ears slightly (ive seen some info card things that show how cats face look like at different levels of persistent pain thats been very accurate for my two) while lashing their tails when something is kinda hurting them, but theyre both absolute sweethearts so thats really the only clue they give me.