Can we do blood sugar testing after meals?

I got into an argument lately with my sister concerning on taking the blood sugar test.  She claims that blood sugar test can be done before and after launch.  I told her what I think about that, most doctor and nurses always said to not to eat anything before taking blood sugar testing, so I believe that this is more accurate than testing after meals.

One day, our mother is feeling weak that we decided to send her to the hospital for check-ups.  We found out that it was because she is having her third stroke.  Her first stroke is back on October, the second one is on November and now the 3rd stroke which we believe is dangerous since our father died when he got his second stroke.  Luckily she didn’t die after her 3rd stroke.

The doctor gave us instructions that we should give her insulin even if the blood sugar is low.  Normally I am doing blood sugar before lunch but since we couldn’t control our mother to not eat before taking a test.  I am forced to do a little research about what my sister and I are arguing before.  I found out that there are blood sugar testing can be done 2 hours after the last time she ate.  It is said that the blood sugar regulates after 2 hours so we could depend on the reading.  Normally if we are going to do the blood sugar testing before meals, the acceptable reading should be somewhere between 90 to 120, but doing it after meals, it should be 120 to 140.