Hello gkanshu,
greetings from healthcaremagic.com
I am Dr Sourav Chakraborty  and i will be helping you with your query.
As i can deduce from your history , you mother have been given some medicine for hear cardiac ailments following which she has developed itching / allergic reactions. However your history is incomplete for me to come to a significant conclusion.
I need to know which drug your 
dermatologist has pointed out as the" culprit one "
And who told you to stop Rancad/ ranolazine her cardiologist or the dermatologist ?
Since you have not revealed such information i will try to list out significant possible interactions of regular drugs used in 
acute coronary syndrome only.
1) Ranolazine/Rancad  is known to interact with 
atorvastatin and increase the concentration of atorvastatin and hence increases the chance of 
thrombocytopenia. 
rhabdomyolysis and 
acute renal failure. Few patients do report rarely itching with atorvastatin but more so with fluvastatin, rosuvastatin, and simvastatin.
2) Ranolazine/Rancad will increase the level or effect of metoprolol/ 
beta blocker  drugs
I do believe  changing the brand of statin /atorvastatin for your mother can help solve the problem or consult with her cardiologist.
Also your mother is showing promising improvement in her cardiac ailments then i do not advocate pausing her cardiac drugs.
Hope i have been able to help you. Take care.