How should i get bills for services taken from a freelancer

Thank u very much sirs.as suggested by you,i am following your advice and asked for invoice and a written contract.

she sent me an invoice by e-mail on microsoft word document,that mentions her home address,mobile no.,two e-mail IDs(one of them was used to e-mail me this invoice),account beneficiary name(her name),Acct no.,bank branch(in delhi),bank name,and IFSC code.it also mentions the contract's terms and conditions.

however this invoice does not have her signature.

she said i should send her the money through online transfer or through bank deposit,to her acct. details.

although she gave her home address,there is no add. proof.once when i asked her for the same,she said she has the add. proof of her hometown which is in kolkata.(where she lived before marriage)

1. is transferring the money thru online transfer or account deposit better,or shud i insist on cheque payment only,which u have advised?is there any way to find out?

3. should i insist on a signed invoice,or invoice sent by e-mail is good enough?

thank you again