Centuries. That's how long Rose had known the Doctor. They'd been bonded for almost that long, and loved each other for the entirety of it. Centuries is time enough to love someone to their core.
That's why Rose was upset. It wasn't that the Doctor had regenerated into a woman. It was the insinuation that Rose was fickle enough to let that change alter her love.
"I'm… I'm so sorry Rose, I don't know what happened. I… you know I've never had good control over these things and I'm just… I wish I could tell you that it was just an aesthetic change but… I feel it. This is me. I'm a woman now."
"Doctor-" Rose tried to interject.
"No, no. It's okay. Do you want me to drop you off in Cardiff? Spend some time with Jack, maybe? I don't know. If this is too much I under-"
"Doctor!"
"Ah. I see. Angry. Yes. Got it. Setting a course."
Rose grabbed her now-wife by the shoulders. "Doctor, look at me." Dark brown eyes gazed back at her own with a golden gleam of fresh regeneration. "I love you, you know that."
The Doctor breathed. "Yes."
"And you still love me, yes?"
Now she looked concerned. "What?! Rose! Of course! I could never-"
"Then nothing's changed," Rose cut her off. "I love you, whether you're a man, a woman, something in between or nothing at all. None of that matters to me. All that matters is that you're you and you love me."
The Doctor's eyes were full of tears. "Oh Rose."
Gently, Rose pressed her lips to the Doctors'. They were soft and warm and pliant. Different, yes, but not more different than any other regeneration. Opening her mouth, she gave the Doctor a quick caress of the tongue and then pulled back.
"See?" she said. "We've still got it."
The Doctor laughed and leaned her head against Rose's.
"Plus," she added. "we've got all new positions to try. I can't wait to torture you with the same techniques you've been using on me for the past hundred years."
The Doctor groaned at that. "Mmm. Time to test this new body out, then?"
Rose smiled. "Lead the way."