My sister was tested positive for covid and whenever i check her oximeter the waves are straight in line in the half oximeter value and only a beat comes up is it something to worry? also while checking blood pressure the heart rate is 55 is it nrm?

Heart rate is on the low side but is normal. Not sure what you’re describing but what is important is that the oxygen saturation is above 92%.

Either the oxymeter does not function or you did not do it correctly. Sometimes, the fingernail is the problem, dark color or artificial fingernail. If the pulse oximeter catches the pulse, the line should be in a wave form. If you see only a straightline, there will be no number of oxygen saturation. Heart rate of 55 is slightly low but it should be fine if her blood pressure is not low.