Common misconception is that it does not need reporting if the profit is below the tax allowance. In fact, if the profit is over £2,500 or gross rents over £10,000, then it is grounds for a tax return.
No. You are misconceived. No-one needs to complete a tax return unless required to do so by notice given to them by HMRC. If a person is not asked to complete a tax return, there can be no penalties for not doing so. A notice must be given for there to be a failure to comply with the notice.
The only requirement where notice has not been given is to tell HMRC if there is a libaility to pay tax. The income must exceed the personal allowance (or gains must exceed the annual exemption).
The OP says that she does not know if her profit exceeds the personal allowance. I find that unlikely. She will know from the regular deposits into her bank account how much she receives. If it exceeds the personal allowance, she should follow the advice given and speak with an advisor. One wonders if she told TC Office that she has rental income?