I might disapprove of Mrs. Clay based on her poor taste in choice of companions--what sensible person would want to pal around with Elizabeth & Sir Walter without an ulterior motive, but there Lady Russell shares the blame as she is with them on a daily basis herself, albeit for different reasons. Mrs. Clay's obsequiousness is repulsive to the reader but I believe is the ticket to being admitted to the rarefied atmosphere of Elizabeth's & Sir Walter's company.

The reason for Mrs. Clay's being brought by Mr. Shepherd might be both because he sees a match as possible & advantageous, but also because she can be moral support to him as he tries to push his points about the need to rent Kellynch, the desirability of the Navy, & the move to Bath.

I can envision a scenario where Mr. Shepherd, from early on, could have brought Penelope to assist with negotiations on other issues by appealing to Elizabeth (he would be aware of Elizabeth's influence on her father) while he worked on Sir Walter. She could have been coached froma a relatively early age on how to "handle" the most powerful Elliots, a skill that she could now be applying to her own ends as well as her Father's.

Personally I see no problem with her efforts given the responsibility all women had to connect themselves as advantageously as possible--barring romantic notions.