While it's not at all dangerous to live with someone who is HIV positive, it would have been nice if she shared that information with you. Just so you know. But in terms of risk for items like sharing a razor, you are not at risk for HIV transmission from objects. Air inactivates the virus. So, any blood on something like a razor will not transmit the virus. The only ways that adults get HIV is from having actual sex that is unprotected and it can be vaginal or anal sex or sharing IV drug needles. Saliva also inactivates the virus so you wouldn't get it from sharing spoons, forks, etc.
But no, sharing a razor with her would not transmit the virus.
You never had to test at all for this. This isn't an HIV risk. EVEN if you had a cut, she had a cut, there was blood on the razor dried or dripping, you'd not get HIV from this as HIV is inactivated by air. Your test at 47 days was negative because you had no risk and any test you take from now on would be negative for the same reason. So, don't waste your time and money.
Really, no worries about this incident. The plastic cover would not make a difference. Air is still involved. No risk.
You have been already offered the support you were seeking from this forum, there is nothing more we could add to GuitarRox's information.
It has been clearly explained to you that you were never at a risk. At this point your behavior is leaning towards anxiety and you must see a counselor to address that.
If this helps you, there has been no recorded case of any one contracting the virus in that manner in history of this disease. The likelihood of you dying right now choking on oxygen is way higher than dying due to contraction of this virus.