I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
Although this may not be a conflict of interest (in fact, nearly usual in small offices, when service is made by mail an attorney will be the notary) the notarization may not be allowed if the affidavit of service is made by a family member.
Even if improper, this is a difficult issue to raise.
The answer provided to you is in the nature of general information. The general proposition being that you should try to avoid a bad outcome if you can.
The attorney can swear the adult resident on-party as to her service of a document because attorneys only prohibition against dual roles is that of witness-advocate. This means the attorney can be the fact witness and the advocate for those facts at the same time. Otherwise, being a notary and a plaintiff's lawyer does not constitute a conflict of interest.