Can a very bad yeast infection cause capsular contracture?

Capsular contracture results from an overzealous immune response to a foreign body. In the case of breast implants, capsular contracture can cause painful distortion of the implant and overlying breast tissue. The Baker scale is used to determine the severity of this response:
Grade 1: Soft, natural appearance
Grade 2: Palpable firmness, natural appearance
Grade 3: Firm, distorted appearance
Grade 4: Firm, distorted and painful
One of the most common causes of capsular contracture is related to contamination of the implant during placement. Biofilm develops on the implant surface (usually from staphylococcus epidermidis, a common skin flora) causing prolonged inflammation and scarring around the implant. "No touch" techniques for breast implant placement (namely, the Keller Introducer) has been implemented to avoid any contact with the implant's surface outside of the body.
Localized infections--including vaginal yeast infections--have not been described to contribute to capsular contracture. Similarly, blood stream or other systemic infections have not been shown to cause scar formation around breast implants.
In addition, subpectoral implant placement ("unders") has been shown to decrease the likelihood of capsular contracture.

There's nothing in the literature that I'm aware of that connects yeast infection with capsular contracture. This is not to say that is not possible just not proven.

Yeast infections are not a cause of capsular contracture.  It is unlikely that this was the cause of your problem.