First heat indicator?

So, my seven month old pup is inching closer to her first heat. So far, I haven't seen any tell tale physical signs, but there is one change thats occurred lately that I wonder if it is an indicator of impending heat.

She's been well potty trained for a few .months now, hardly any accidents inside anymore.

However, for the last few days she's been very purposefully going inside when im not looking. Even after a walk (where she'll both poop and pee), and plenty of regular intervals of outside time. She's also not signaling as she normally does before doing this. She'll sneak away and do it when I'm not looking.

Is this a regular indicator of heat coming on? I know she's still very young, but its definitely confusing because she does signal throughout the day, and then will go outside, but it seems like at least once a day for the last few days she'll save some up specifically for going inside.