I don't think Steffi will be losing any sleep over what Martina Navratilova has to say.
Steffi came along in 87, when Navratilova and Evert were still leading the tour, and began to wipe the floor with both of them. She then won the Golden Slam, a feat neither women achieved. For Navratilova, this would have been hard to take. Whatever we want to say about the Grand Slam, it is considered by many to be the ultimate achievement. Tennis is measured in seasons and to withstand the pressure of winning all four Majors in one season, with all that Media interest, is the mark of a GOAT. It is also highly unlikely that a Grand slammer is not going to do anything else after that achievement, as Graf's fellow Grand Slammers demonstrate.
The point is that the jealousy started then and got worse and worse as Graf's Major tally increased. And then came the stabbing and the criticism of Steffi and how she handled it and how it inflated her career achievements. And it was the perfect ammunition for Navratilova, seeing the 23 year old Graf with 11 Majors and well on her way to surpassing 18, to use to belittle Graf and argue against her being the Goat.
But really, what else was Graf supposed to have done? Retired? Crumbled under all the criticism? No wonder the already quiet Graf kept silent. All Graf could do was what she had always done: turn up and play. She did and she doubled her Major haul and sent herself to the top of at least half of the tennis analyst's GOAT list.
And as for Graf being unpopular in her time. She was enormously respected by the tennis elite who mostly approved of her letting her racket do the talking. And the crowds loved her too. I don't think there is anyone posting here who has not seen the '96 and '99 French Open finals.
Graf has those memories of her celebrated wins as well as her own private thoughts on what happened to Monica and how it affected her own career. She has every right to both of them and every right not to share them just as Martina has her right to unleash her venom, venom which will most likely go uncared for by the one whom it was directed at.