She's the right age for a small dog to first go into heat.
Like was mentioned: Stop bringing her to the park. She's going to suddenly encourage the behaviour when she's ready, and it'll come to you as a surprise when she ties and has a litter at 6 months of age. I'd be extra careful and REALLY make sure she's well and done before letting her interact with dogs again. This includes dogs on walks-it can be really fast for them to tie, and once they do you can't pull the male off. If you look up some breeding info...it can be VERY painful for the female if you try to pull him off, and in her state of heat she WANTS to be tied with. <Insert "Just because you can doesn't mean you should" talk to any 12 years old child here>
I know you don't need THAT talk but if you apply it to this context it really blooms. XD
She'll also be telling the interested males off for the first bit (maybe they get as sore as we do!) but it does change very fast. You may not notice the tie until its too plate if you aren't careful to prevent issues, and at her age a litter wouldn't be in her best health interests either. I'm all for spaying late, but separation and management are your best friends for the next while.
Second thing: If your male dog is not neutered, now is the time to consistently separate them. It's not worth the risk. It's the same thing.
She may not have too much discharge-the first few heats are usually lighter than the rest. The discharge also only comes around the end of the heat, so you wouldn't get it during this stage either. Grab a diaper thing for when it happens to keep your house from getting pretty gross. You should be able to google dog in heat diaper and get the idea. The first heats also tend to be shorter-it likely won't go a full month as it does in some adult dogs. Some encouragement to get through dealing with the rotation of your dogs as it will likely get frustrating if you haven't been particular about keeping them apart.
The peeing could be a totally separate issue from being in heat, or a minor side effect of having a swollen uterus for a small dog-I'm not sure. If it's manageable and you can just take her out more frequently I would do that. You can always call your vet if you're unsure and ask questions, this isn't really the type of thing you need to go in for but they typically are very generous answering generic questions like this on the phone.
TL;dr Start doing research now, this sounds like a dog going into their first heat. If you're still unsure, call a vet and ask some questions. You likely don't need to go in but they should be willing to educate.