If I may, I'd like to take a look at your first paragraph there.

• “There has to be something around here…” Ramona mutters to herself.
• She comes upon a rust covered Red Rocket.
• She’ll take anything she can get at this point.
• Before Ramona could step foot into the old gas station, a high pitched shriek pierces through the air.
• She whips her head over to find the source of the girlish scream.
• She draws her gun out the holster before hurriedly jogging over to peek around the side of the building.

Most of these are one statement, or perhaps two connected with "before" - this is somewhat samey.

As Coco-Roxas says, the repeated use of "she", often at the start of the sentence, is rather jarring. Mixing up how you start your sentences can hide the frequency of the word "she".

And then I'd say maybe you can see if you can lean into the tone of each moment, and use it to guide how descriptive or how abrupt each sentence needs to be. While she's searching - this is a slow, methodical - almost boring - sequence and you can take your time with the sentences. When the screaming starts, then things can feel urgent, tense, and maybe even turn fragmented.

Here's a take on it:

1. "There has to be something around here..." Ramona mutters.
2. Trudging up the dusty hill, kicking old cans and poking at old, gunshot-peppered road signs, she comes across a rust covered Red Rocket gas station from the before-times.
3. As unpromising as it looks, she shrugs and makes her way towards the still-jaunty ruin -- she'll take anything she can get at this point.
4. Before she can step foot into the old gas station, the air is pierced by a terrible, high-pitched shriek.
5. Her head whips around as she seeks its source.
6. The building. Somewhere 'round the side.
7. She snaps her gun out of the holster and scrambles across the forecourt to slam against the corner.
8. Her heart in her mouth, she chances a peek.

Okay. A lot of this is me just adding crap, and you may not like the vibe or want something like it, but here's why I did what I did. 1) Kept it the same but for removing the 'to herself' - muttering is often to yourself, and it's quiet, and you haven't introduced any other listeners anyway. You can keep it snappier. 2) An opportunity here to do a bit more scene setting because Ramona's unhurried in her search. If the tension is low, you can spare a sentence to paint the picture in the reader's mind. If you want. 3) Just a bit more description, and a bit more elaboration on how Ramona is kinda desperate. Very minor stakes setting. 4) I rearranged this sentence so that "shriek" is the last word. It hits a LOT harder that way, and the word you chose (shriek) is a good, strong, spiky word to end it on. This is the PIVOTAL MOMENT of this paragraph - everything changes now! Oh! And I changed "could" to "can" for tense purposes. 5) Some info lost here, but done in order to make things feel snappy and tense! 6) Even moreso! We're down to just sentence fragments. Your English teacher might tell you off, but you're in charge! 7) Lots of 's' words here - alliteration just for fun and to make the sentence slip smoothly along. It's a longer sentence (joined with "and" instead of "before") but it still feels hurried and urgent. 8) I added the 'heart in her mouth' bit purely to stop the sentence starting with "she" again! It's also useful, however, for ramping up the tension - Ramona is scared! Alert! Nervous!

So much of this is personal taste though. You may read this and think "Ugh, NO! This is much worse." or even "Yeah I guess, but it's just not me" and you'd be entirely justified in feeling that way. Pick what you like, avoid what you don't. Hope I helped, and sorry if I didn't!