Cliff Notes:
https://marvel.fandom.com/wiki/Incre...Hulk_Vol_1_138
https://marvel.fandom.com/wiki/Incre...Hulk_Vol_1_141
https://marvel.fandom.com/wiki/Incre...Hulk_Vol_1_168
Betty had been turned into glass by a blood transfusion by Sandman. Doc Samson was a regular human, who offered to cure the Hulk by removing his gamma and in doing so, save Betty. Samson used that energy to become Doc Samson. Later MODOK kidnaps Betty and transforms her into the Harpy.
Basically, at this time she's got a lot of weird radiation running through her body at this time period.
Years later, Betty is killed (poisoned by Abomination, but Bruce thinks it was due to years of exposure to his radiation) and kept in stasis. The Intelligencia (Leader, MODOK, etc) make a deal with Gen. Ross to save Betty. They turn him into Red Hulk and the same to Betty.
So, presuming all of these changes/radiations mixing we're seeing a return of Harpy, but in a red form, sort of a halfway point between the two gamma forms (theorizing..)
Rick similarly had multiple gamma forms (Hulk, A-Bomb) so it should be interesting what results.