It is entirely normal and understandable to feel uncomfortable when your personal boundaries are being crossed, especially when it comes to something as private and sensitive as therapy. Recommending your therapist to your friends, including your best friend, can make you feel like your safe and confidential space is being invaded, and it's okay to feel that way.
Your feelings are valid, and you are not being selfish for wanting to maintain some control over your therapy space and keep it separate from your personal relationships. It's essential to have a sense of autonomy and privacy in your therapeutic journey, and having someone close to you see the same therapist might compromise that.
It would be a good idea to talk to your mum about your feelings and concerns. Let her know that you appreciate her intention to help your friends by recommending a therapist, but you also need your therapy space to remain personal and separate. Explain that it makes you uncomfortable to share the same therapist with your best friend and that you would prefer if she didn't make further recommendations to people you are close to.
Setting boundaries is a healthy and necessary part of maintaining your emotional well-being, and it's okay to advocate for your needs. A good therapist will understand the importance of confidentiality and the potential impact of having overlapping clients from the same social circle. They should respect your boundaries and work to ensure that your therapeutic space remains private.
If the situation doesn't improve, and you still feel uncomfortable, you might consider discussing this with your therapist directly. They are ethically bound to maintain your confidentiality and may have a process in place to address such concerns.
Remember, seeking therapy is about taking care of yourself, and you have every right to prioritize your feelings and needs in this process.