|I liked reading this story. I could picture the wedding dress shop and the feelings being evoked from the characters.
Below are my suggestions:
1) You wrote:
I can do this, she silently insisted. Even if Mom doesn’t have time, I can do this.
It might be better to say her mother isn't there than to say her mother doesn't have time:
I can do this, she silently insisted. Even if Mom isn't here, I can do this.
This fact helps the reader know up front that her mother's absence is a major factor in her feelings.
2) You wrote:
“Let’s ask her if she wants to look any more today or if she wants to have lunch and go home.” Karri moved to Trina’s side, touching the taller woman’s shoulder. “Trina, do you want to leave, have lunch, and forget shopping today?”
Here, I felt you could streamline this more. It's sort of redundant. Maybe remove the first sentence:
Karri moved to Trina’s side, touching the taller woman’s shoulder. “Trina, do you want to leave, have lunch, and forget shopping today?”
Her eyes never leaving the tapping, twirling spoon, Trina answered, “I want a more traditional gown than I seen so far.
I think you meant:
Her eyes never leaving the tapping, twirling spoon, Trina answered, “I want a more traditional gown than I have seen so far.
4) You wrote:
Trina gasped before starting to rummage through the dozen or so dresses.
Trina's gasping isn't explained. Did she gasp because she was pleased, or because of the number of dresses?
Also, the word gasping somehow doesn't fit here. You also use it a few sentences later, and explained it well there:
The sales clerk gasped, “You do look beautiful. That dress looks like it was made for you.”
“My son will think you make the dress look gorgeous,” Marie replied.
For some reason, I expected her to say:
“My son will think you make any dress look gorgeous,” Marie replied.
This implies that her son is so in love with her, that she would look gorgeous in any dress.
After lunch, the three women returned to the bridal shop. When they entered this time, a saleswoman greeted them. “May I help you with something?”
“This young lady,” Marie nodded toward Trina, “wants a more traditional dress than the ones displayed or on the racks here.”
“Oh, we have some old-fashioned types toward the back. If you’ll follow me, we’ll look there.” The clerk led them to the rear of the shop, where she pointed to a rack of billowing wedding gowns, many lace-covered satin.
I felt this also could be more streamlined. The reader already knows Trina wants a traditional wedding dress, so you don't need to repeat it in the dialogue to the saleswoman. Here is my version:
After lunch, the three women returned to the bridal shop and asked the sales clerk to see the traditional dresses.
“The old-fashioned types are in the back,” said the sales clerk, leading them to the rear of the shop, where she pointed to a rack of billowing wedding gowns, many lace-covered satin.
Overall, I felt the beginning was very detailed in the wedding shop. And the part about Trina's parent's was short. I'd like to see more development of the characters of Trina's parents. They sound like self-centered people. Play that out. Make the reader feel what Trina is feeling - that her parents don't care about her.
Hope this helped!