My tenant owes rent but how can i prove it? CA?

Behind my house is another house which is rented out. The tenant has been there for years with no problem until a year ago when the landlord who is also my father ped away. Since then the tenant has been short on payments and now owes around 3000 dollars. If i evict her, will i be able to get my money even though the proof may be insufficient. She has verbally agreed to paying what she owes and acknowledges that but all VERBALLY! I live in California and dont have many rent reciepts because i only started using them since she started getting dep in debt with me.