English doesn't have any native feminizing suffixes: all the ones we typically use (-a, -ia, -ette/etta, -ine/ina) are borrowed from Latin and Latinate languages.
Rather, Old English had certain elements that were exclusively masculine or exclusively feminine (and many that could be either). It also usually depended on whether that element was the first half or the second half of the name--for instance, hild ("battle") could start either a boys' or girls' name (like Hildewine "battle-friend" or Hildegard "battle protection"), but as a ending element, it was pretty much exclusively for girls.
So instead, if you wanted to endemically turn an OE boys' name into a girls' name (whether or not that was something that even occurred to them, IDK), you would have to swap out the masculine ending element for a feminine one similar in sound or meaning, like Ælfwig ("elf war") to Ælfhild ("elf battle"); or Wulfwine ("wolf friend") to Wulfwynn ("wolf joy"); or in some cases, just reverse the elements: Burgstan ("fortress stone") to Stanburg ("stone fortress"); or Thrudgar ("strength spear") or Gertrude ("spear strength").
Of course, the whole "add an A to make a girls' name" thing was imported pretty darned early (by the 800s for sure, but possibly as early as the 200s AD), so this whole thing is really just an exercise in dorky minutiae. :p