[Swampcollie]

No sign of swelling.

I have a nine-month-old as well and have to keep an eye on her. Her mother is due in season anytime now, so they are under close watch.

When your pup starts her first season, the vulva will swell, and the nipples will change their size to those of an adult. After her cycle is complete, they will not return to puppy size but stay at the normal adult size. Most of my girls over the years have swelled to the point that their vulva is the size of a small lemon and is readily observed from behind as they are walking away. (It's Obvious)
Be aware that many females do not have their first heat cycles until well into their second year.

 

[Swampcollie]

She may have a UTI. That will also influence how other dogs react to her because her scent is changed.

 

[Swampcollie]

She's going through puberty.

Heat cycles do not progress like clockwork, every girl is a little different and sometimes it progesses in starts and stops. It sounds like your girl is starting her cycle but keep in mind the first one brings a lot of physical changes with it. Those changes take time.